Reciprocating internal combustion engines include an engine block that defines a plurality of bores. A piston assembly is moveably disposed within and supported by each of the bores. The piston assembly includes an annular body having an outer surface that defines at least one groove. A split compression ring defining a ring gap is disposed within each of the grooves.
Prior to installation into the bore, the ring is disposed in an uncompressed condition, i.e., a free state, and includes an uncompressed diameter that is larger than a diameter of the bore. In order to install the piston assembly into the bore, the ring is compressed to define a diameter less than the diameter of the bore. Once installed, the ring expands radially into contact with the bore.
The ring is radially expandable out of the groove and into abutting engagement with the bore. The ring seals against the surface of the bore as the piston assembly reciprocates within the bore. However, oil may still leak past the ring through the ring gap, or at the interface between ring and the bore.